When a cataract is removed, the patient’s naked eye vision usually does not exceed 0.02 because the lens, a natural convex lens, is missing from the refractive system, and this vision cannot meet the patient’s needs for living, learning and working.
For a long time, it has been common to wear thousands of degrees of farsighted glasses to correct vision after cataract surgery. This is because before the introduction of corneal contact lenses and IOLs, it was the only method used to correct aphakic eyes.
It is undeniable that glasses help patients’ vision a lot, but there are also some insurmountable disadvantages, especially after cataract removal in one eye, wearing a convex lens of 1000 degrees, the object image is 22%-33% larger than the original one, while the object image seen in the other eye is obviously smaller. Due to the poor image in both eyes, patients have severe diplopia and dizziness, and most of these patients give up wearing the lenses and use only the unoperated eye to see objects, thus having no sense of stereo.
After bilateral cataract surgery, patients wearing high convex lenses will have spatial disorientation due to the magnification of objects, especially in the early stage of lens wear, they may not be able to find the key to open the door or spill the ink bottle when sucking ink. In addition, the difference in refractive power between the central and peripheral parts of the high convex lens and the trigeminal effect can produce spherical aberration when viewed obliquely, resulting in displacement of objects, causing a sense of dislocation and distortion of spatial orientation. Of course, these shortcomings can be partially overcome with the patient’s efforts and after some time of adaptation.
However, the narrowing of the peripheral visual field that occurs after wearing a high convex lens is very difficult for patients to overcome, and objects between 50 and 65 degrees of the visual field cannot enter the eye, forming a circular blind spot. This not only brings inconvenience to the patient, but may even bring danger to the patient.
Later, corneal contact lenses were introduced to make up for the lack of wearing lenses. However, corneal contact lenses have to be removed, cleaned and disinfected every day, which is inconvenient for children and the elderly. Improper use of contact lenses can also damage the cornea or lead to corneal inflammation.
In this regard, IOLs are the most ideal method of correction. Patients who receive IOL implants not only have improved vision in the naked eye after surgery, but also have restored the highest level of binocular vision, namely three-dimensional spatial awareness, also known as stereopsis, to the operated eye.